There is continuously increasing need for precise, non-destructive, non-contact, or remote chemical analysis of selected targets and samples, as well as analysis of distribution of the tested components within the target or sample. This may include identification of chemical composition of the stars or planets, aerial terrestrial reconnaissance, remote pollution detection, remote detection of explosive traces in luggage of airplane passengers and many other applications where chemical analysis of the remote target has to be performed, with exact localization of the point in space were analysis was performed. With scale exception, a similar problem arises in microscopy where the distribution of some chemical components across the microscopic samples has to be determined. Hence, in both cases there is a need for spatial distribution analysis of chemical components across certain large or small areas. In many cases this can be achieved with spectroscopic methods, which extract required information on chemical composition variations from analysis of radiation generated or effected by analyzed adjacent or non-adjacent points of targets or samples. Typically, the radiation from these points is collected by the means of some light collecting optics and delivered to some kind of spectrum analyzer. In the past such analyzers were not able to perform simultaneous analysis on a number of points so that the analysis was performed consecutively point by point. Spatial selectivity of such system was determined by the capability of applied light collecting system, while spectral performance of the system was determined by the performance of both light collecting as well spectrum analyzing components of the instrument
The need for detailed quantitative image analysis, especially in astronomy and microscopy has been recognized long time ago for may years, a large number of many photometric and spectrophotometric instruments have been developed, designed and produced. Description of some of these devices as applied in microscopy, developed before year 1980, can be found in book of “Advanced Light Microscopy” (Vol. 3 Measuring techniques) by M. Pluta and in other books and articles. The devices developed before the time of the above publication could not take advantages provided by arrays of photodetectors, which did not exist at that time. To achieve required performance, very sophisticated instruments had been developed and were produced by leading producers of the microscopes. The majority of these instruments were designed for absorbance measurement of microscopic samples, and hence used monochromatic light to illuminate them. As a result, measurement systems of such kind were not able to perform spectral analysis of radiation transformed by the microscopic sample by fluorescence, Raman scattering, phosphorescence or similar effects. For these types of objects, devices able to analyze the spectral composition of the radiation affected by different areas of the microscopic samples are required. In the past, this problem was resolved by consecutive spectral analysis of radiation produced or affected by the sample point by point. Such a point by a point spectral analysis has many disadvantages and many methods have been developed for simultaneous extraction of spectral information for number of adjacent or non-adjacent points of the object or its image produced by some optical imaging system. The systems performing such analysis on a number of adjacent points are usually referenced as imaging spectrum analyzers or imaging spectrometers, while the systems performing the analysis on non-adjacent points are usually called multi-channel spectrum analyzers or multi-channel spectrometers.
In this description both systems will be referred to as imaging spectrometers, while the term multi-channel spectrometer will be reserved specifically to situations when the fact that analyzed radiation has been collected from spatially non-adjacent points is important. There exist a large number of both imaging and spectrum analyzing instruments, which can be used for this purpose.
Similar problems exist in all areas of spectroscopy applications, where information on spatial spectral variability of target or sample are required.
The problem of simultaneous analysis of radiation at different points of targets and samples or their optical images can be addressed in many different ways, depending on the particular needs and technical capabilities available, as will be described below. A method to convert ordinary microscope into a high performance spectrometric system, able to analyze the spectra in a set of adjacent or non-adjacent image points by means of a line imaging spectrometer is disclosed.
Taking into account a large variety of both imaging and spectrum analyzing instruments, a question arises as to how to select and couple instruments from each group to achieve the best possible performance of the final arrangement. Therefore, this is the first object of this invention to provide technical tools and methods for analysis of performance of both imaging and spectrum analyzing instruments to provide the best coupling between them, with an exemplary application to microscopy.
State of the Art in Field of Imaging Spectrometers
The use of imaging spectrometers, allowing for the spectral analysis of radiation transformed by the sample as a result of some physical process, form a mature class measurement method, which have found various technical implementations. There exist instruments with two dimensional image capturing detectors (human eye, photographic film, 2-D array of the photodetectors), which apply spectral band-pass filters placed somewhere in the optical path between the object and the detector to allow radiation within a certain spectral range to reach the 2-D detector. The filters can be consecutively changed to select the radiation, which corresponds to different spectral bands. It is a quite common solution in fluorescent microscopy, for example, and many instrument based on this principle are already available on the market. This is clear that while such filtering provides valued information, the amount of information obtained in such a way is limited by the number of filters, which can be practically used. Recently, several different solutions have been proposed to facilitate the process of spectral band selection. These include continuously moved variable interference filters; interference filters, produced with holographic or thin layer technology, whose spectral band pass can be adjusted by changing the filter inclination to the incident light beam; acousto-optic tunable filters (AOTF), whose spectral band pass is determined by frequency of the acoustic wave applied; liquid-crystal tunable filters, whose spectral band pass is determined by applied voltage; Fourier transform spectrum analyzers, which, by means of a variable optical path interferometer, encode the spectral information in a form of a correlation signal which in an additional step mathematically can be transformed into spectral information. Recently these methods have been enhanced with Hadamard transform spectrometers performing local wavelength coding by mean of small dedicated local diffractive optical elements working in conjunction with 2-D detector array, the signal from which mathematically can be de-convolved into local spectral information. Since both spectral and spatial information are simultaneously coded and registered using the information capacity of the same 2-D detector array it is clear for those skilled in the art that this is achieved as a compromise between spatial and spectral information capacities. All these methods are complemented with line imaging spectrometry, able to provide high quality spectral information for a set of points aligned along a straight or curved slit. Because of recently achieved unsurpassed spatial and spectral performance, this technique is particularly useful for precise spectroscopic analysis of the various targets and samples. To be able to take full advantage of such a technique; however, the optical coupling of the line imaging spectrometer to the imaging system such as microscope becomes highly important. In principle two coupling methods are possible: the direct coupling of the imaging system to spectrometer through the projection of an image produced by the imaging system onto a slit plane of the line imaging spectrometer and coupling the light from the image plane of the imaging system to the slit of the spectrometer by the means of optical fibers.
Therefore, it is the primary objective of this invention to provide means for efficient transfer of radiation between the image plane of the imaging system and the spectrometer slit plane providing either the highest possible spatial and spectral resolution for an image line using direct image projection by the imaging system onto the slit plane of a line imaging spectrometer or by providing a flexible connection and freedom in selection of the analyzed points of the microscopic sample using fiber-optic connection between the imaging system such as telescope or microscope and line imaging spectrometer. The second objective of the invention is to provide fiber optic connection between the imaging system such as telescope or microscope and line imaging spectrometer with spatial configurations of fibers different from the spatial configuration of fibers in the spectrometer slit plane. The third objective of the present invention is to provide means to perform spectral analysis of samples observed with different imaging systems by a single line imaging spectrometer. The fourth objective of the invention is to provide means to perform spectral analysis of the samples in a single or plurality of imaging systems by the means of a number of spectrometers, each of which performs the analysis in different spectral ranges. These and other advantageous solutions related to coupling one or a number of imaging systems to one or a number of line imaging spectrometers will become apparent from following detailed description of the invention, attached drawings and claims and sub-claims of the invention.
In this description coupling of the microscope to line imaging spectrometer will be used as an example, but the same principle can be used for coupling any imaging system, producing a real optical image, to the line imaging spectrometer.